Concrete Calculator
How much concrete do you actually need? This free concrete calculator gives DIY homeowners and remodeling pros instant cubic-yard, 60 lb bag, and 80 lb bag counts for slabs, driveways, footings, post holes, stairs, walls, and columns — all from one form.
Concrete mistakes are expensive. Order too little and your pour stops mid-job; order too much and you pay short-load fees plus disposal. A small math error on a 4-inch slab can leave you 3 bags short or 6 bags over — every single time.
Built-in ACI 318 waste factor, support for ready-mix and bagged products, and side-by-side bagged vs. truck-delivery cost — in seconds, no signup.
Professional Concrete Calculator
Industry-standard material calculations based on ACI, IBC/IRC, and DOT specifications.
Project Type
Dimensions
Specifications
Residential driveways, garage floors, standard slabs
About This Calculator
Industry Standards
- ACI 318 structural concrete code
- International Building Code (IBC/IRC)
- DOT specifications for driveways
- ASTM material standards
Key Specifications
- 60 lb bag yields 0.45 cu ft
- 80 lb bag yields 0.60 cu ft
- 1 cubic yard = 27 cubic feet
- Standard waste factor: 5-10%
Professional Note: This calculator provides estimates based on industry standards. Always consult local building codes, obtain necessary permits, and consider hiring a licensed contractor for structural projects. Actual material requirements may vary based on site conditions, formwork, and installation methods.
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▶ Watch: How to Calculate Concrete (Slabs, Footings & Posts)
For a standard 4-inch thick slab, you need 1.23 cubic yards of concrete per 100 square feet. An 80-pound bag yields 0.60 cubic feet, requiring 45 bags per cubic yard.
Essential Tools
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View Product (paid link)📊 Concrete Volume by Project Type
Standard Slab (4")
Driveway (6")
Footings (12" deep)
Posts (12" diameter)
📐 Industry Standard Specifications
Bag Yields (ASTM C150)
| Bag Size | Cubic Feet | Bags per Yard |
|---|---|---|
| 80 lb bag | 0.60 cubic feet | 45 bags |
| 60 lb bag | 0.45 cubic feet | 60 bags |
| Cubic yard | 27 cubic feet | — |
Thickness Requirements (IBC/IRC)
Residential Applications
- •Patios/Walkways: 3.5 inches minimum (4" standard)
- •Garage floors: 4-5 inches (6-8" for heavy vehicles)
- •Driveways: 6 inches minimum
- •Foundation walls: 6-8 inches
Footing Depth
- •Frost zones: Below local frost depth
- •Non-frost areas: 12 inches minimum
- •Always verify with local building department
⚠️Waste Factors (ACI 301)
🧮 Step-by-Step Calculation
Example: 10' × 20' Patio Slab (4 inches thick)
🚛 Ready-Mix vs. Bagged Concrete
Ready-Mix Concrete
Delivered by truck
When to use:
- ✓Projects requiring 1+ cubic yards
- ✓Large slabs, driveways, foundations
- ✓Any project over 50 bags
Advantages:
- • Professionally mixed to specifications
- • Consistent strength throughout
- • Faster pour for large projects
- • Cost-effective over 1 yard
Bagged Concrete
Mix-on-site
When to use:
- ✓Small repairs under 1 cubic yard
- ✓Post holes, small footings
- ✓Multiple pours over time
Advantages:
- • Mix only what you need
- • No minimum order
- • Store unused bags
- • Better for small projects
📋 Common Concrete Projects
10' × 10' Patio (4 inches)
Two-car Driveway 20' × 20' (6 inches)
50-foot Sidewalk (4' wide, 4 inches thick)
Four 12-inch Diameter Deck Posts (4 feet deep)
💪 Concrete Strength Specifications
PSI Ratings (ACI 318)
(Most common)
👷 Professional Standards
🕐Curing Requirements (ACI 308)
- 7Minimum 7 days moist curing for full strength
- 24Avoid foot traffic for 24 hours
- ✓Full weight-bearing after 7 days
- 28Maximum strength achieved at 28 days
🌡️Temperature Requirements
📚 Building Code References
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Related Code Guides
Building code, climate zone, and standards references that change defaults for this calculator.
Climate Zone 3: R-Value Requirements (2021 IECC)
Warm Climate Zone 3 R-value minimums for the Carolinas, Georgia, central Texas, Arizona, and the Mid-South under the 2021 IECC.
Climate Zone 4: R-Value Requirements (2021 IECC)
Mixed-humid Climate Zone 4 R-value minimums for the Mid-Atlantic, Ohio Valley, Kentucky, Tennessee, and northern Texas under the 2021 IECC.
Climate Zone 8: R-Value Requirements (2021 IECC)
Subarctic Climate Zone 8 R-value minimums for most of Alaska under the 2021 IECC and Alaska Building Energy Efficiency Standard.
Frequently Asked Questions
What is a cubic yard of concrete?
A cubic yard is 27 cubic feet of concrete (3 feet × 3 feet × 3 feet). This is the standard measurement for ready-mix concrete delivery. One cubic yard weighs approximately 4,000 pounds and covers 81 square feet at 4 inches thick.
How many 80-lb bags of concrete do I need per cubic yard?
Each 80-lb bag yields approximately 0.6 cubic feet when mixed. One cubic yard requires 45 bags of 80-lb concrete mix. For 60-lb bags, which yield 0.45 cubic feet each, you need 60 bags per cubic yard.
What thickness should a concrete slab be?
IRC code requires 3.5 inches minimum for residential slabs-on-grade. Standard practice is 4 inches for garage floors, patios, and basement slabs. Driveways carrying passenger vehicles need 4-5 inches, increasing to 6 inches for RV and heavy truck traffic. Always verify local building code requirements.
Why add waste factor to concrete calculations?
ACI recommends 5-10% waste factor for spillage, over-excavation, uneven subgrade, and form irregularities. Simple rectangular slabs typically need 5-7% extra. Complex pours with multiple sections, steps, or difficult access require 10-15% waste factor.